Module 3 Section 1: Exchange and Transport

Question 1

Substance exchange in cells

Answer 1

Cells need to take in things like oxygen and glucose for metabolic reactions
They need to excrete waste products from these reactions like carbon dioxide and urea

Question 2

What decides the difficulty at which substances can be exchanged in cells

Answer 2

The surface area : volume ratio

Question 3

How to find SA : V ratio of cuboid 4 x 4 x 2

Answer 3

Volume: 2 x 4 x 4 = 32cm3
Surface area: 2 x 4 x 4 = 32cm2 ( top and bottom surfaces )
+ 4 x 2 x 4 ( four sides of the cube )

Question 4

Why do multicellular organisms need exchange surfaces

Answer 4

In multicellular animals, diffusion across the outer membrane is too slow because:

Some cells are deep inside the body - there’s a big distance between them and the outside environment

Large animals have a low surface area to volume ratio - its difficult to exchange enough substances to supply a large volume of animal through a relatively small outer surface

Multicellular organisms have a higher metabolic rate than single celled organisms, so they use up oxygen and glucose faster

Question 5

why don’t single celled organisms need exchange surfaces

Answer 5

In single celled organism, these substances can diffuse directly in or out of the cell across the cell surface membrane.
The diffusion rate is quick because of the small distances the substances have to travel

Question 6

How are root hair cells adapted for exchange of substances

Answer 6

Large surface area:
Cells on plant roots grown into long hairs which stick into the soil, each root branch will have millions of thee hairs
This gives the roots a large surface area which helps increase the absorption of water by osmosis and mineral ions by active transport

Question 7

How are alveoli adapted for exchange of substances

Answer 7

Short diffusion pathway:
Each alveolus is made from a single layer of thin, flat cells called alveolar epithelium
O2 diffuses out of the alveolar space into the blood, CO2 diffuses out
The thin alveolar epithelium helps to decrease the distance over which O2 ad XCO2 diffusion takes place and increases the rate of diffusion

Good blood supply:
surrounded by large capillary, giving each alveolus has its own blood supply. blood constantly takes oxygen away and bring carbon dioxide to the alveoli

Good ventilation:
Lung ventilated so air in each alveolus is constantly replaced

Question 8

Features of exchange surfaces to improve efficiency

Answer 8

Large surface area
Thin
Good blood supply or ventilation

Question 9

How are fish gills adapted for substance exchange

Answer 9

Large surface area

Good blood supply:
Large network of capillaries which keeps them well supplied with blood

Well ventilated:
Fresh water constantly passes over them

This maintains the concentration gradient of O2 which increase the rate at which O2 diffuses into the blood

Question 10

Structure of the lungs

Answer 10

As you breathe in, air enters the trachea
Trachea splits into two bronchi - one bronchus leading to each lung
Each bronchus then branches off into smaller tubes called bronchioles
Bronchioles end in small sacs called alveoli where gas is exchanged
Ribcage, intercostal muscles’ and diaphragm all work together to bring air in and out

Question 11

Function of goblet cells

Answer 11

Secrete mucus
The mucus traps microorganisms and dust particles in the inhaled air, stopping them from reaching the alveoli

Question 12

Function of the cilia

Answer 12

Cilia ( on the surface of cells lining airways ) beat mucus
this moves the mucus upward away from the alveoli towards the throat where it is swallowed

Question 13

Function of elastic fibres

Answer 13

Elastic fibres in walls of the trachea, bronchi, bronchioles and alveoli help process of breathing out
On breathing in, the lungs inflate and the fibres are stretched, then recoil to push air out during exhalation

Question 14

Function of smooth muscle

Answer 14

Smooth muscles in trachea walls, bronchi and bronchioles allows their diameter to be controlled
Smooth muscle relaxes during exercise and makes tubes wider
Creates less resistance to airflow and air can move in and out of lungs more easily

Question 15

Function of rings of cartilage

Answer 15

Rings of cartilage in wall of the trachea and bronchi
Provide support
Strong and flexible to stop trachea and bronchi collapsing when you breathe in and pressure drops

Question 16

Structure of trachea

Answer 16

Large C shaped rings of cartilage
Smooth muscle
Elastic fibres
Goblet cells
Ciliated epithelium

Question 17

Structure of Bronchi

Answer 17

Smaller rings of cartilage
Smooth muscle
Elastic fibres
Goblet cells
Ciliated epithelium

Question 18

Structure of larger, smaller and smallest bronchioles

Answer 18

Larger:
Smooth muscle
Elastic fibres
Goblet cells
Ciliated epithelium

Smaller:
Smooth muscle
Elastic fibres
Ciliated epithelium

Smallest:
Smooth muscle
Elastic fibres
Ciliated epithelium

Question 19

Structure of alveoli

Answer 19

No cartilage
Smooth muscle
Elastic fibres
Regular epithelium ( no cilia )

Question 20

Process of Inspiration

Answer 20

The external intercostal and diaphragm muscles contract
This causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thorax
As the volume of the thorax increases, the lung pressure decreases to below atmospheric pressure
This causes air to flown into the lungs
Inspiration is an active process - it requires energy

Question 21

Process of expiration

Answer 21

The external intercostal and diaphragm muscles relax
The ribcage moves downwards and inwards and the diaphragm becomes curved again
The thorax volume decreases, causing the air pressure to increase to above atmospheric pressure
Air is forced out of the lungs
Normal expiration is a passive process - it doesn’t require energy
Expiration can be forced ( e.g. blowing or sighing ), this is when the internal intercostal muscles contract to pull the ribcage down and in

Question 22

What does tidal volume mean

Answer 22

The volume of air in each breath - usually about 0.4dm3

Question 23

What does vital capacity mean

Answer 23

The maximum volume of air that can be breathed in or out

Question 24

What does breathing rate mean

Answer 24

How many breaths are taken - usually in a minute

Question 25

What does oxygen consumption or oxygen uptake mean

Answer 25

The rate at which an organism uses up oxygen ( e.g. the number of dm3 used per minute )

Question 26

How can a spirometer be used to investigate breathing

Answer 26

A spirometer has an oxygen filled chamber with a movable lid
The person breathes through a tube connected to the oxygen chamber
As the person breathes in and out, the lid of the chamber moves up and down
These movements can be recorded by a pen attached to the lid of the chamber - this writes on a rotating drum, creating a spirometer trace. Or the spirometer can be hooked up to a motion sensor - this will use the movements to produce electronic signals, which are picked up by a data logger
The soda lime in the tube the subject breathes into absorbs carbon dioxide

Question 27

What happens when a fish opens it’s mouth

Answer 27

The fish opens its mouth, which lowers the floors of the buccal cavity ( the space inside the mouth )
The volume of the buccal cavity increases which decreases the pressure inside the cavity.
Water is then sucked into the cavity

Question 28

What happens when a fish closes it’s mouth

Answer 28

When the fish closes it’s mouth, the floor of the buccal cavity is raised again
The volume inside the cavity decreases, the pressure increases, water is forced out of the cavity across the gill filaments
Each gill covered by a bony flap called the operculum ( which protects the gill )
The increase in pressure forces the operculum on each side of the head to open, allowing water to leave the gills

Question 29

Structure of a fish’s gas exchange system

Answer 29

Water containing oxygen, enters the fish through its mouth and passes out through the gills
Each gill is made of lots of thin branches called gill filaments or primary lamellae, which provide a large surface area for exchange of gases
The gill filaments are covered in lots of tiny structures called gill plates or secondary lamellae, which increase the surface area even more
Each gill is supported by a gill arch

Question 30

How do fish use a counter-current system for gas exchange

Answer 30

Blood flows through the gill plates in one direction and water flows over in the opposite direction
This is called a counter current system
It maintains a large concentration gradient between the water and the blood
The concentration of oxygen in the water is always higher than that in the blood
So as much oxygen as possible diffuses from the water into the blood
Always a preferential conc gradient

Question 31

How does the gas exchange system work in insects

Answer 31

Insects have microscopic air-filled pipes called tracheae which they use for gas exchange
Air moves into the tracheae through pores on the insect’s surface called spiracles
Oxygen travels down the concentration gradient towards the cells
Carbon Dioxide moves down its own concentration gradient towards the spiracles to be released into the atmosphere
The tracheae branch off into smaller tracheoles which have thin permeable wall and go to individual cells
The tracheoles also contain fluid, which oxygen dissolves in
Insects use rhythmic abdominal movements to change the volume of their bodies and move air in and out of the spiracles
When larger insects are flying, they use their wing movements to pump their thoraxes

Question 32

Why is a concurrent exchange system worse than a countercurrent

Answer 32

Blood flows parallel to water flowing over the gills
Initially there is a very steep concentration gradient
As oxygen poor blood passes the oxygen rich water
However, an equilibrium is reached and diffusion then stops

Question 33

How do insects maintain aerobic respiration in increasingly anaerobic conditions

Answer 33

Anaerobic respiration leads to build up of lactic acid in the muscle tissues
As a result, water is drawn out of the tracheoles by osmosis ( lower water potential in cells )
Reduces volume of tracheal fluid in the tracheoles
This exposes more surface area in the tracheoles
Allows more oxygen to be absorbed

Question 34

How to find oxygen uptake, tidal volume and vital capacity on a spirometer graph

Answer 34